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Solar USB Charger 


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Solar USB Charger 

Written By: Steve Hobley 


Heat gun (1) 
or pocket lighter. 

Multimeter or Continuity Tester (1) 

Soldering Iron. 15- Watt (1) 
from RadioShack. 

Wire cutter/stripper (1) 


Solder, lead-free (1) 
from RadioShack. 

Rectifier diode assortment 25 piece (1) 
from RadioShack. 

Zener diode. 5.1V. 1N4733A (1) 
from RadioShack. 

Solar cell, encapsulated module (1) 
from RadioShack. 

Extension cable. USB A/A (1) 
from RadioShack. 

Heat shrink tubing. 6" (1) 
from RadioShack. 


Charge up your USB devices with the power of the sun. By adding a small solar panel and 
two diodes to a standard USB cable, you can plug that cable into USB devices needing a 
recharge. It's so easy. Let's get started. 

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Solar USB Charger 

The Solar USB Charger being tested on a sunny day 

Check out more Weekend Projects . 

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Solar USB Charger 

• Cut the end off of a USB extension cable. You will need the female end. 

• Cut away the cable's outer insulation and isolate the power lines. These are the red wire 
(+5v), and black wire (Ground). Strip the ends. 

• The solar panel already has corresponding red (+) and black (-) wires. 

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Solar USB Charger 


Cut a 2-3" piece of 1/4" heatshrink tubing and slide it over the cut end of the USB cable. 

Cut a similar piece of 1/8" tubing and slide it over either the red or the black wire coining 
from the solar cell. This tubing will insulate the wiring connections from each other. 

Pick a rectifier diode from the pack; any one of them will do. Solder the diode between the 
red wires from the solar cell and the USB cable, with its cathode leg (that's the negative 
side, marked with the stripe) facing the USB side. 

Solder the two black wires directly together. 

Solder the smaller, red and black Zener diode across the two wire connections, with its 

black stripe facing the red wire side. 

Slide the heat shrink tubing over the joints and shrink with a heat gun or lighter. 
(Hold the lighter flame over the tubing, rather than under, and move the tubing 
around to shrink all spots.) Always put the tubing on first, before you solder! 

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Solar USB Charger 

• The rectifier diode eliminates 
incorrect polarity and prevents 
power from being drained from 
USB devices. The Zener diode 
protects them by preventing power 
surges over 5V (actually 5.1V). 

• To test your charger's output, place 
the solar panel in the sun and plug 
the cut-off end of the USB cable 
plug back into the other end. Use a 
multimeter to probe the voltage 
between the red and black wires. 

• Depending on how sunny a day it 
is, your multimeter should show 
something between 4V and 5V. The 
Zener should prevent anything from 
going too far above 5V. 

• I have used this device to charge a 
5V USB battery pack. If you want 
to charge an iPhone, you will need 
to implement this modification that 
raises one of the other USB pins to 
2.7V. The iPhone uses this as a 
signal to detect charging. 

• You can see video of the testing of 
the device in the intro section of 
this project. 

If there's one thing we have in the US, it's sunlight. And where I live, the summers can get 
incredibly hot. It's a shame to let all of that free energy go to waste, and this project shows you 
how easy it is to put that solar power to use. 

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Solar USB Charger 

This document was last generated on 201 3-01 -26 08:58:20 AM. 

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